Head trauma represents a spectrum of injury ranging from concussion through contusion, diffuse axonal injury, penetrating injury, and disruption of blood vessels with intracranial hemorrhage, as well as other brain conditions and diseases. These traumatic brain events lead to brain swelling as a result of evolving edema and threaten the sufficiency of blood flow to the brain, leading to further hypoxic-ischemic injury. This increased swelling manifests itself in a changing brain compliance (or conversely cerebral elastance) and can be represented as the relationship between intra-cranial pressure (ICP) and pulsatile regional cerebral blood flow (rCBF) waveforms. Certain conditions, or disease states, manifest a risk for “secondary injury” after the primary insult in the form of increased water volume content (swelling) which can be referred to as cerebral edema. These include head trauma, hydrocephalus, stroke, and brain tumor among others. Therefore, a significant aspect of management of clinical deterioration in these conditions is the monitoring of brain edema and treatment in an effort to minimize its harmful effects. Beyond head trauma, similar alterations in cerebral perfusion and ICP can follow in other pathologic conditions afflicting the brain such as hydrocephalus, stroke, brain tumor, and seizures.
Due to cranial constraint upon the swelling brain, intra-cranial pressure (ICP) may quickly deteriorate as the brain herniates across internal openings of the cranium such as the tentorium or the foramen magnum at its base. ICP increases in an exponential-like pattern within increasing intra-cranial volume in the form of brain edema, CSF, or blood. This relationship is referred to as the pressure-volume index (PVI). As the PVI deteriorates, the stiffness of the brain worsens, a condition called poor brain compliance, or its inverse, abnormal brain elastance. A goal of therapy is to identify and reverse worsening brain compliance within best potentials of aggressive therapy. The cranium is occasionally partially removed to give the brain more room to swell during the acute secondary injury phase. In addition to ICP monitoring, the clinician observes in order to recognize regional brain edema and its advancing pattern, influencing the therapeutic decision process. Frequent imaging using prior techniques is not optimal or practical management due to the risks to the patient of transport and the exposure of irradiation.
In an effort to improve early detection, and therefore treatment, of the patient with risk of increasing cerebral edema, multiple attempts have been explored. Portable CT scanners have been developed which eliminate the need of transport of the patient from the intensive care unit (ICU) to the radiology department. However, the method is still intermittent and is associated with increasing radiation dose.
Well recognized imaging modalities of human tissues can also be employed, such as Magnetic Resonance Imaging (MRI) and Ultrasound (US). However, MRIs are relatively impractical for use in acute TBI assessment because it does not image bone well and data acquisition is lengthy. Also, the static magnetic or changing RF fields used for imaging severely limit existing transducer and ventilator devices due to encumbrance or risk for burns or induced electrical currents into tissues.
Traumatic brain injuries require monitoring, as the ICP can increase and the cerebral perfusion can be altered into harmful range as a result of the injury or other condition. Uncontrolled intracranial pressure can result in irreversible damage, or even death. Existing systems lack the ability to continuously monitor brain compliance. Single snapshots of the state of the brain are not sufficient if damage is indicated in the initial scan, or if clinical status worsens. It is, therefore, desirable to provide a system that continuously monitors a patient by continuously mapping a brain image and displaying brain compliance. Furthermore, recognition of worsening injuries may be accomplished by continuously monitoring intra-cranial pressure and blood flow, as opposed to single snapshot views.
Additionally, external sensors have been applied in prior attempts to measure the electrical properties within a brain. However, this does not provide an accurate reading of the electrical properties, because only the surface or superficial region of the cerebrum is addressed. The signals generated by and between the electrodes are not capable of fully penetrating an internal organ to accurately portray its condition via monitoring and mapping its electrical properties. There is a need for a system that continuously and accurately monitors an internal organ such as a brain, or another internal organ, so as to provide the condition of the internal organ.